In the use of the microdispenser set out in our previously granted U.S. Pat. Nos. 3,606,086 and Re 27,645, a fixed volume of fluid may be delivered by the microdispenser by permitting the plunger thereof to travel through the entire length of its stroke. Fixed volumes of fluid of lesser amount may also be delivered by placing inserts within the barrel of the microdispenser, to shorten the length of the plunger stroke and correspondingly reduce the amount of fluid drawn into the capillary tube. However, the microdispenser of our previous invention is particularly adapted to handle very small amounts of fluid, and it is extremely difficult to deliver the predetermined amounts of fluid with the precision required in some laboratory work, since small deviations in the amounts of fluid drawn into the capillary tube can occur when parts of the microdispenser are replaced, or for other reasons.